German and Swiss authorities have carried out raids seizing documents after learning a German private detective had investigated the MH17 air disaster, Dutch officials and media said on Tuesday.
Among the objects seized during last week's raids were "apparently explosive papers" which Dutch investigators hope may narrow down the search for those behind the 2014 tragedy, said the daily De Telegraaf.
All 298 passengers and crew -- the majority of them Dutch -- died when Malaysia Airlines flight MH17 was hit by a Russian-made BUK anti-aircraft missile while flying over war-torn eastern Ukraine on July 17, 2014.
The Boeing 777 was en route from Amsterdam to Kuala Lumpur.
"It's possible that the suspected culprits behind the firing on MH17 may have been in contact with" the detective's office, de Telegraaf said, citing what it said was the Netherlands' request to Swiss authorities for help.
According to the Dutch paper, the private detective was paid some €17 million ($19mn) by a rich donor -- whose identity remains unknown -- to investigate the causes of the crash.
Identified only as Josef R., the detective began his inquiries two months after the disaster, having been initially promised a fee of some €30mn.
"We are hoping to get some information about this. That's why the raids at his home were carried out," the spokesman for the prosecution service, Wim De Bruin, told AFP.
After the private eye's home in Bad Schwartau in northern Germany was searched, a safe deposit box in a bank in Zurich, Switzerland, was also emptied and its contents seized.
"We don't actually know what was in the box. The Swiss judge must now decide if its contents can be handed over to Dutch officials," de Bruin added.
The news comes after Dutch investigators on Monday released an update on their inquiry to the families of the victims. It included pictures of fragments of the BUK missile found at the crash site.
The same pictures were also included in the final conclusions of the initial Dutch-led international investigation, which determined in October that the flight was shot down by the Russian-made missile, fired from an area in eastern Ukraine held by pro-Russian separatists.
Now a criminal investigation in the Netherlands is underway to identify exactly who fired the missile and where from, even though many believe that those to blame will never be arrested and tried.
The first official findings by the criminal investigators are now expected after the summer, as they await further information from Russia.